Method for producing non-aging rimmed steels



United States Patent 2,999,749 1 METHOD FOR PRODUCING NON AGING" RIMMED. STEELS Earle R. Saunders, Hudson, Ohio, and Russell M. Frank New York, and Carl A. Beiser, Lewiston, N.Y., assignors to Union Carbide Corporation,v a corporation of New York v No Drawing. Filed Sept. 17, 1958, Ser. No. 761,456

11 Claims. (Cl. 7558) I This invention relates to a method for. the preparation of non-aging rimmed steels. r

The problem of producing a deep-drawing steel stabilized against age-hardening effects has been consistently high on the list of problems dealt with by industry. It has been long recognized thatnitrogen is the principal element which causes the age-hardening phenomenon in steel. At the present time, most of the steels produced for deep-drawing applications are treated in the molten stage by the addition of strong deoxidizers such as aluminum, titanium, or zirconium. These elements are added in precise and predetermined amounts to effect complete deoxidation and produce what is known in the industry as a killed steel. In these steels, aluminum is most commonly used to completely deoxidize the steel and atv the same time precipitate the nitrogen in theform of aluminum nitrides, thereby preventing the nitrogen from' dissolving in the alpha iron to eventually precipitate as iron nitride. As opposed to iron nitride, which precipitates at room temperature. and thus may alter the properties of the steel when stored, nitrides of aluminum, titanium, and zirconium' precipitate at relatively high temperatures so that essentially all of the nitrogen is tied up by the time the ingot is cool. Thus, once the metal is fabricated, no significant amount ofiaging can occur due to the nitrogen effect even though it is stored fo'rlfextended lengths of time." The disadvantages of aluminumkilled steels are the relatively. low yields due to hot-top losses and a tendency toward erratic surface, qualit to entrapment of alumina at ornearthe, surfac The disadvantages inherent 1 in killed stels ar not present in rimmedsteelsf In-the preparation of rimmed steel, as a result of the reaction between oxygen andfcarbon while the metal is solidifying in the ingot, the molten metal etfervesces, giving oif a large volume of carbon monoxide, and forming deep-seated blow holes in the final ingot which are eliminated during hot working. This eliminates the need for hot-topping, and, in

general, considerably less loss of metal is incurred with rimmed steel ingots than with killed steels since less crop-' ping is necessary. In rimmed steels, however, the-nitrogen is in solution in the ferrite and it is believed that during storage unstable iron nitrides form and aging results. Aging is manifested byincreased strength and; hardness, by decreasing toughness and ductility, and, in some cases, by the return :of a distinct yield point in cold-worked material.

It has been proposed that non-aging rimmed steels be Patented Sept. 12, 1961 2; mation of the products of the reaction minus'the sum of the free energy change of formation of the reactants of thereaction; As applied to the carbon reduction of FeO at 1600 C. on a molar basis, the following has been.

If the free energy change of the reactionbetween the added element or elements with the iron oxide is more negative than ,.32,000 calories per mole, the rimming action will be inhibited to a great extent, orcompletely stopped if the affinity of the element for oxygen is excessively high. Under such-conditions, a killed steel would result. Conversely, if the free; energy change of the reaction is less negative thanv '32,000 calories per prepared by adding selected nitride forming elements -I= while the steel is in the molten state. The nitride-former, however, must not have such superior deoxidizing properties as to cause the steel to be killed. Production of;

a non-aging rimmed steel, therefore, depends upon :the

addition of a nitride-forming element which does not ap'i Workable addi= preciably inhibit the rimming action. tives may be selected by using the rimming reaction FeO-i-C CO+Fe as the standard. l v i g The free energychange '(AF)' of the reaction of this equation is the sum of the free energy change of the formole,the. rimming action would proceed and a non-aging rimmed steel would be produced. The four elements listed'below have nitride-forming tendencies and, when reacting with iron oxide, have a free energy change re; 7 actionless negative than that produced by the carbon.

reduction of iron oxide to form carbon monoxide: I

Columbium Tantalum Vanadium Boron Other elements are available asnitrideformers which meet the requirements outlined above, such as silicon and chromium, but these are not feasible either for economic or technical reasons. 7 I

Various experimenters have heretofore attempted to produce non-aging rimmed steels by the addition of elemental vanadium or boron. These attempts have failed to meet with success. Vanadium behaves erratically in stabilizing nitrogen and, since recoveries of the metal are poor, it is also expensive to use. The use of boron alone involves very critical control due to the small amount required to achieve non-aging characteristics. Certain other of the above additives, especially those of low specific gravity, have low recoveries attributable primarily unalloyed, elemental form or in small quantities.

It is, therefore, the primary object of this invention to provide an improved method for the preparation of non-aging'rimmed steels. 7

Other objects are to provide such a method whereby columbium, tantalum, vanadium, and boron maybe efliciently added to steel melts, singly or in combination, to

provide such anon-aging rimmed steel.

The, above objects are achieved by providing a molten bath of nitrogen-containing steel, adding to said molten bath an addition agent comprising at least 25 percent manganese and at least one element selected from the group consisting of columbium, tantalum, vanadium, and

boron inv anlamount suflicient to combine with the free nitrogen insaid steel.

'An elementwhich is known to be a good nitrideformer, and, is otherwise suitable for producing non-aging rimmed steels, may be added to steel more efilciently from "arrecovery and distribution viewpoint when such an ele- I ment is 'alloyedwith, or is present as a component in a bonded mixture with, manganese. Other physical properties such as wear resistance and a lowering of hardening temperature are also improved by the presence of this element. With respect to the present invention, however, manganese is essential because of its dual roles as diluent and distributor of difiicult-to-handle reactive elements. The simultaneous addition of manganese is an important feature of the present invention and makes possible the attainment of. more uniform distribution, decreased criticalness of additive amount, and better recoveries of the nitride-forming element. Since manganese is normally added in the ladle, the method of the invention will most commonly be carried out after the molten steel has been tapped into the ladle. Supplementary nitride-formers and/or deoxidizers, as well as other important alloying constituents, may be added at the same time.

Example I As an example of the method of the invention, assume a steel having a manganese content in the open hearth between 0.10 and 0.12 percent by weight; As sume a desired final manganese content between 0.30 and 0.35 percent, and assume additionally that a normal 85 percent recovery of manganese will be achieved. For

'these conditions, the addition agents added in the practice of the method of the invention should add from approximately 42 to 5.9 pounds of manganese per ton of steel tapped. Next, assuming a nitrogen content of 0.004 percent (deep-drawing, open hearth steel usually contains between 0.003 and 0.005 percent nitrogen) in a steel whose base composition is 0.07 percent carbon, 0.35 percent manganese, 0.01 percent silicon, 0.03 percent maximum phosphorus, and 0.04 percent maximum sulfur, any nitride-forming element or combination of elements must be added to a level of 0.0159 atomic percent (0.004 percent by weight nitrogen=0.0159 atomic percent nitrogen) times the ratio of the atoms of nitrideforrning element to nitrogen atoms in the stable nitride that is formed.

Conversions may, therefore, be made on the four nitride-formers referred to above, to the following weight percentages, based on the steel composition of the example and a nitrogen content of 0.004 weight percent.

The weight percent figures in the above table are derived by multiplying a conversion factor which, on the basis of the nitrogen content of the steel, is equal to 0.000283, by the atomic weight of the element in question.

The calculated amounts given, however, are not those actually used in the practice of the invention. For example, at least twice as much vanadium is required to produce a non-aging steel. This additional quantity is necessary as the excess combines with oxygen, sulfur, and carbon, to form inclusions or dissolve in the steel. A quantity in excess of that which unites chemically with other constituents in the steel is required to be present for forming nitrides. Using the above weight percentages and knowing the oxide-, carbideand sulfide-forming tendencies of the elements in question, it is, therefore, possible to provide approximate multiplication factors for each of the elements as is done in the following table. Also indicated in this table are the expected recoveries of each element to account for losses of the addition agent components to the slag or those attributed specifically to added and if nitrogen is present in an amount approximating 0.004 percent by weight:

Thco- Element retical Multlpli- Expected Required Nitride-Former Addition, cation Recovery, in Addi- Weight Factor Percent tion,

Percent Lb./Ton

It is to be understood that the manganese content of the addition agent may be derived from any source. For example, elemental manganese or ferromanganese may be used with equally satisfactory results. Similarly, the sources of the nitride-forming elements are equally varied. These elements may be incorporated with the manganese in their elemental states or as alloys. Ferrovanadium may be combined with ferromanganese to form an addition agent for use in practicing the method of the invention, for example.

If the nitride-formers listed above are added individually in their elemental states to medium carbon ferromanganese comprising 80.0 percent manganese, the addition agents ofthe example would have .the following composition:

' Manganese, Nitride- Iron, Per- Element Percent Former, cent Percent 67 17 Bal. 58 30 B211. 72 10 Bal. 79 1. 72 Ba] The above example has illustrated the manner in which addition agents may be composed for practicing the method of the invention with a specific steel containing 0.004 percent nitrogen and requiring a manganese addition of approximately 5.5 pounds per ton. If the steel composition varies from that assumed in Example I, the addition agent may be varied accordingly.

Example 1! Assume .a steel having the same manganese requirements as that of Example I. Assume nitrogen contents of 0.002. and 0.005 percent for purposes of calculation.

The weight percent requirements of each element are as follows:

account the same multiplication factors and expected recovery percentages used in Example I are as follows:

Theoret- Expected Element ical Ad Multipli- Recov- Required Nitride-Former dition, cation cry, Per in Addi' Weight Factor cent tion Lb./

Percent Ton Columbium 0.013 1. 04 1 0.033 2 g 75 1. 74 Tantalum 0.026 1.39 0.065 2 75 3. 48 Vanadium 0.007 0.38 0. 018 2 75 0. 96 Boron i 0.001 0.04 0. 004 1. 5 75 0. 16

. c Mangaa I Nitride- Iron, Element nese, Former, Percent Percent Percent Columbium 40-75 --a0 Ba]. Tantalum- 30-05 2540 Be]. Vanadium"-.. 45-80 520 Bal. Boron 5085 1-4 Bal.

Example 111 Anexample is given here of a complexing calculation when it is desired to incorporate more than one nitrideformer with manganese for use in the practice of. the method of the invention. The steel is similar to that of Example I.

Assume that for economic reasons it is desired to use vanadium and /3 boron.

Because there exists 0.0159. atomic percent nitrogen in the steel, there must exist an equal amountof effective nitride-formers.

of elements thatare primarily deoxidizers and only see ondarily nitride-formers may be complexed with the pri-' mary nitride-formers. Elements falling into this cate :gory might include zirconium, titanium, beryllium, magnesium, aluminum, calcium, silicon and/or barium. Since even the nitride-formers oxidize to varying extents, these reactive elements would preferentially deoxidize and-desulfurize and thus increase the amountof the main nitride former that would be available for tying up the nitrogen. This practice would also increase the recovery of (the main element, and, therefore, a lesser;,addition of this element would be required. It is' proposed, therefore, that the more reactive elements maybe add'e'd'to. any of the manganesebase addition agents in an amount up to 12.5 percent. The total amount of each nitride-former is not afiected by such addition although, of course, its percentage amount in the addition agent is thereby decreased.

The inclusion of manganese as a major constituent of the addition agents usedin the practice of the invention serves to eifectively distribute the nitride-forming elements in the melt whereby better control may be achieved.

Best results are obtainedif manganese. is present in the I addition agent in the amount of at least 25.0 percent.

- 'Asexamples of the effectiveness of the method of the invention, the followingsteel heats were produced utilizing as addition agents a ferromanganese-boron alloy, and a manganese-vanadium-aluminum-titanium combination, the latter being produced both as an alloy and as (.0159) =0.0106 atomic percent vanadium; I a So1-type product, that is, a bonded mechanical mixl (.0159) =0.0053 atomic percent boron. ture.

Steel Composition Produced, Percent Heat N0. Additive A1 Mn Si O N T1 V B 1 Nolan rimmed steel 0. 014 0.25 0. 01 0.052 0.004 2 2-3%B1nFeMn .0005 0.54 0.03 Y 0.15 0.002 0.007 3.. V, 80% Mn, 7% A1, 0013 0.34 0.02 0 09 0. 005 0.01 0. 046

10% T1 Alloy. 4 40% V, 30% Mn, 7% A1, 0. 013 0.37 0. 03 0.004 0. 01 0.04

10% Ti bonded mlx- I ture.

Convert to weight percentages: Heat No. l was included as a base. heat for the sole purpement V "1 pose of comparison. Heat No. 2 shows. the results of at wt V utiliiing a boron addition vvithfmangane'se as the carrier 0.0106 Wt. percent V and heats 3 and 4show'theresults of vanadium additions, Wt V with manganese in the low range, where minor amounts 1 v n of primary deoxidizers areemployed in combination with welgm.peroent 15000973 V the nitride-former. M f. j V When tested at diiferent temperatures for tensile 00053: V strength, samples of the above steels yielded the follow- 1.80+Wl7. percent B ing results:

at. wt. V weight percent B=.00103 Using multiplication factors and expected recoveries,

the following'percentages of vanadium and boron must be added to the steel:

On a per ton basis, the following is required: 0.52'lb.

Wt. percent V= =0.026

Wt. percent B= =0.00206 V; 0.04 lb. B. 5

I A Tensile'Strength, p.s.i.

HeatNo. 5 a .Room

Tempera- At 400 F. Change ture 7 -To those skilled in the art, is obvious that the deoreasein tensile strength on specimens tested from room temperature to 400- F- shows that the steel produced by the addition agents of the invention have excellent non: aging properties. Thusi'manganese may be added simultaneously'and in intimate relationship with the nitrideformers, with or without deoxidizers, to produce nonaging rimmed steel.

still another point of view. For example, small amounts 35 When samples of the heats were vprestrained to 7 percent elongation at room temperature and aged to 212 F. for 1 hour, the following results were obtained:

Aged 1 Hour at 212 F.

Heat. No.

Stress at Yield Aging 7% Elong. Strength, Index p.s.i.

' such amounts a-s not to interfere with the rimming action,

ingots are produced which have good surface quality. In addition, manganese need not be added separately to bring the manganese content up to specification. The addition of complex addition agents also serves to produce better recoveries and more complete dispersion of the individual components of the alloys or bonded mixtures falling within the scope of the present invention.

As used in the appended claims, the term major constituen of manganese refers to an amount of manganese not less than 25 percent by weight of the addition agent.

Although the above description and examples have been primarily predicated upon the treatment of steel having 0.002 to 0.005 percent by weight nitrogen content,

it is to be understood that the invention is not so limited. The addition of manganese base agents within the scope of this invention may be practiced with equal effectiveness in the treatment of steels to be utilized for deepd-rawing applications having any nitrogen content.

What is claimed is: p

l. A method for the production of non-aging rimmed steel which comprises providing a molten bath of steel,

adding to said molten bath an addition agent comprising at least 25 percent manganese and at least one element selected from the group consisting of columbium, tantalum, vanadium, and boron in an amount sufficient to combine with the nitrogen in said steel.

2. A method for the production of non-aging rimmed steels which comprises providing a molten bath of steel, adding to said molten bath an addition agent comprising at least 25 percent manganese, at least one element selected from the group consisting of columbium, tanta- 4. A method for the production of non-aging rimmed steel which comprises providing a molten bath of steel, adding to said molten bath an addition agent comprising at least 25 percent'manganese and up to a of about 5.9 pounds of manganese per ton of stee nd"1.0 to 2.0 pounds columbium per ton of said steel.

5. A method for the production'of non-agmgrimmed steel which comprises providing a molten 'bath of 'steel, addingto said molten bath an addition agentcomprising' at least 25 percent m'ang aneseandup to a maximunrof about 5.9 pounds of manganese per ton'of steel, and 1.0 to 4.0 pounds of tantalum per'ton of said steel.

6. A method for the production of non-aging rimmed steel which comprises providing a moltenbath of steel, adding to said molten bath an addition agent comprising at least 25 percent manganese'and up to a maximum of about 5.9 pounds of manganese per ton of steel, and 0.3 to 1.0 pound vanadium per ton of said steel.

7. A method for the production of non-aging rimmed steel which comprises provid ng a molten bath of steel, adding to said molten bath an addition agent comprising at least 25 percent manganese and up to a maximum of about 5.9 pounds of manganese p 1'- 'ton of steel, and0.'03 to 0.20 pound boron per ton ofsaid steel. g 1

8. A method for the production of non-agin'grimmed steel which comprises providing a molten 'bathof steel, adding to said molten bath anaddition agent comprising at least 25 percent manganese and upto a maximum of about 5.9 pounds of manganese per ton of steel, 1.0 to 2.0 pounds columbium per ton ofsaid steel, and the balance substantially all iron.

9. A method for the production of non-agingrimmed steel which comprises providing a molten bath of steel, adding to said molten bath an addition agent comprising at least 25 percentmanganese and up to a maximum of about 5.9 pounds of manganese per ton of steel, 1.0 to 4.0 pounds of tantalum per ton of said steel, and the balance substantially all iron.

10. A method for the production of non-aging rimmed steel which comprises providing a molten bath of steel, adding to said molten bath an addition agent comprising at least 25 percent manganese and up to a maximum of about 5.9 pounds of manganese per ton of steel, 0.3 to 1.0 pound vanadium, and the balance substantially all iron.

11. A method for the production of non-aging rimmed steel which comprises providing a molten bath of steel, adding to said molten bath an addition agent comprising at least 25 percent manganese and up to a maximum of about 5.9 pounds of manganese per ton of steel, 0:03 to p 0.20 pound boron per ton of said steel, and the balance lum, vanadium, and boron in an amount suflicient to combine with the nitrogen in said steel, and up to 12.5 percent of an element selected from the group consisting of zirconium, titanium, beryllium, magnesium, aluminum, calcium, silicon, and barium.

3. A method for the production of non-aging rimmed '1 steels which comprises providing a molten bath of steel, adding to said molten bath an addition agent comprising at least 25 percent manganese, at least one element selected from the group consisting of columbium, tantalum, vanadium, and boron in an amount suflicient to combine with the nitrogen in said steel, up to 12.5 percent of an element selected from the group consisting of zirconium, titanium, beryllium, magnesium, aluminum, calcium, silicon, and barium, and the balance substantially all iron.

substantially all iron.

References Cited in the file of this patent UNITED STATES. PATENTS V J Strauss Aug. 4-, 1942 .2,356,450. Epstein Aug. 22,:1944 2,370,289 Chandler Feb. 27,'l945 2,771,651 Morgan et al. Nov. 27, 1956 OTHER REFERENCES 

1. A METHOD FOR THE PRODUCTION OF NON-AGING RIMMED STEEL WHICH COMPRISES PROVIDING A MOLTEN BATH OF STEEL, ADDING TO SAID MOLTEN BATH AN ADDITION AGENT COMPRISING AT LEAST 25 PERCENT MANGANESE AND AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF COLUMBIUM, TANTALUM, VANADIUM, AND BORON IN AN AMOUNT SUFFICIENT TO COMBINE WITH THE NITROGEN IN SAID STEEL. 